Method of electrophotography employing a heat glossing composition



Feb. 26, 1963 H. G. GREIG 3,079,253

METHOD OF ELECTROPHOTOGRAPHY EMPLOYING A HEAT GLOSSING COMPOSITION .Filed June 19. 1957 2 Sheets-Shut 1 @LLAA LLAA.. k2!

I NVENToR. HAR nl G. GREIG Feb. 26, 1963 H. G. GRI-:IG 3,079,253

METHOD oF ELEcTRoPHoToGRAPHY EMPLOYING Y A HEAT GLossING coMPosITIoN Filed June 19, A1957 2 sheets-sneer 2 2 3 mm mm 59 ffy.;

JNVENToR. HAROLD G GREIG BY/Qffzad,

4 fron/fr Unite rates Patent O 3,079,253 METHOD E ELECTRPHO'IQGRAPHY EMPLOY- ING A I-EAT GLSSING CMPOSKTN Harold G. Greig, Princeton, NJ., assigner to Radio Corporation of America, a corporation of Delaware Filed .lune 19, 1957, Ser. No. 666,6l0 l Claim. (Cl. 96-l) This invention relates to compositions and recording elements that are prepared with a matte surface finish and which can be converted subsequently to a gloss surface finish solely by heating. Recorded information on the surface of the recording element is `fixed thereto during the heating step.

IMatte surface finish compositions for recording elements have been previously reported. Such compositions may comprise a particulate pigment suspended in a vehicle. For one type of matte surface, .the pigment particles extend irregularly from the surface of the coating, thereby imparting an abrasive quality and matte appearance to the surface. This abrasive quality may be used for recording information thereon as by rubbing a pencil, crayon, stylus, etc. across the surface thereof. Subsequent to recording, it is often desired to tix the recorded information so that further information may be added only with difficulty and so that the recorded information may be removed only with difficulty. Previous processes tix such recorded information by coating with an adhesive or by fusing the information to its support.

In an electrostatic printing process of the type described in C. I. Young and H. G. Greig, ElectrofaX-Direct Electrophotographic Printing on Paper, RCA Review, volume l5, No. 4, pages 469 to 484 (December .1954), a powder image of a predetermined configuration is prepared Iby electrostatic means. rl`he powder image is temporary vand must be fixed -to a support. lPrevious processes coated an adhesive upon the powder image and the support therefor, or selected =a fusible powder for the image and fused the powder to its support.

The use of `an adhesive generally requires special equipment and additional time and technique for its success. Fusing the information to a support also requires special equipment .and technique, and does not gloss the composition or prevent additional marking from being added subsequently.

An object of this invention is to provide improved compositions and recording elements which are prepared with a mat-te surface finish and which can be subsequently converted to a gloss surface finish solely by the application of heat.

Another object is to provide improved compositions and recording elements which are adapted to receive information and, solely upon the application of heat, to ix the information already recorded, and to prevent the addition of further information thereto.

A further object is to -provide -improved processes for preparing the improved compositions and recording elements of the invention.

The compositions of the invention comprise generally a particulate pigment, such as zinc oxide, and up to 2O wei-ght percent of a low-melting particulate material, such as calcium stearate, suspended as separate phases in a vehicle therefor. The proportions of pigment, lowmelting material and vehicle are selected to provide a matte surface finish. The recording elements herein may comprise the foregoing composition upon a support, such as aluminum foil or paper. The recordings element herein may also comprise a support coated with a low- .3,079,253 Patented Feb- 25, 1963 melting materia-l which in turn is over-coated with a com. position having a matte surface -tinish comprising a particulate pigment suspended in a vehicle. Information may be applied to the surface .of the composition by abrasion as with a pencil =or stylus, by transfer, or by electrostatic printing. Upon applying heat, the surface of the composition glosses and the information residing thereon is fixed thereto. Further information is .not easily accepted by and iixed information is not easily removed from the glossed surface.

Compositions and recording elements herein which are useful in electrostatic printing, preferably comprise a particulate photoconductor, `such .as zinc oxide having a surface photoconductivity higher than about l0f9 ohmsvl/ square/ watt/cm.2 yat about 3900 A., and up to about l() weight percent of a low-melting particulate material suspended `as separate phases in an electrically-insulating, film-forming Vehicle.

The Irecording elements `of the invention may be prepared by one of two improved processes. By one process, the vehicle is dissolved in a solvent therefor, and the pigment and low-melting material suspended in the solvent solution. The suspension is then coated Ion .a support. Then the solvent is removed from the coated suspension at temperatures below the glossing temperature of the coating. By the second process, a support is coated with the low-melting material. The vehicle is dissolved in a solvent therefor and the pigment suspended in the solvent solution. The `suspension is then overcoated on the low-melting coating. Then the solvent is removed from the overcoating at temperatures below the glossing temperature of the coating.

The invention is more fully described in the following detailed description when read in conjunction with the accompanying drawings in which:

FIGURES y1(Lz), 1(b), and 1(c) are sectional, elevational views of one recording element of the invention 4before rand after lglossing,

FlGURE 2 is a sectional, elevational view of another recording element of the invention,

FIGURE 3 is a partially-schematic, sectional view of an apparatus for producing a blanket electrostatic charge upon a recording element herein,

FIGURE 4 is a partially-sectional, elevational view of an apparatus for projecting light to form a contact image upon the charged recording element of FIGURE 3, and

FIGURE 5 is a sectional view of an apparatus for developing an electrostatic image upon the recording element produced in FIGURE 4.

Similar reference characters are applied to similar structures throughout the drawings.

In its broader aspect, the invention herein comprises the addition, as a separate phase of up to 20 weight percent `of a low-melting material to a composition comprising `a particulate pigment suspended in a vehicle. The proportions of pigment to vehicle are selected to provide a 4matte finish surface to the composition. Because of the abrasive quality of the matte surface, the coating can be written upon by abrasion as with a pencil or stylus. And, due to the nature of the Writing, the writing may be erased or otherwise removed or other writing may be added. Due to the presence of the low-melting material, heat applied to 4the composition converts the matte iinish surface to a gloss 'finish surface. This conversion fixes the writing to the surface and renders diflicult the addition Iof further writing and removal of fixed writing. In addition to Writing, information may be added by transfer from another surface, by conventional printing techniques, or otherwise applied tothe surface of the -improved compositions herein.

The solvent is then removed from the coating at temperatures below the glossing temperature of the coating.

EXAMPLE 1 An example will illustrate the foregoing type of recording element. A recording element is prepared by coating a paper support with the following suspension:

Grams (1) Zinc oxide (Florence Green Seal-8) 120 (2) Calcium stearate 5 (3) Piccopale-lUO resin 38 (4) Toluene 118 (5) Piccolastic A-5 resin 5 (5) Tricresyl phosphate The Piccopale-lGO (softening point about 100 C) Piccolastic A-5 and tricresyl phosphate are dissolved In the toluene. The calcium stearate is then added and the slurry warmed -to 80 C. The calcium stearate goes into colloidal suspension at about this temperature. The zinc oxide is added after the suspension has cooled and is dispersed by mixing, as in a Waring Blender. This mix. is coated on a paper support by conventional techniques and then dried to remove the toluene at temperatures below the glossing temperature of the coating, which is about 100 C. Referring to FIGURE l(a), the recording element comprises a support 21 of paper having a coating 23 on one surface thereof of `a composition of the invention.

The coating 23 so produced has a matte finish due to zinc oxide particles 22 which extend irregularly from the surface of the coating. The coating may be marked with a pencil, crayon, metal stylus, coin, or other abrasive means. The particles, left behind may be removed with a rubber eraser or other means. If it` is desired to tix the markings .to the paper, the paper is placed in a small oven and heated to above 100 C. for about half a minute. Referring to FIGURE 1(b), the zinc oxide particles 22 and the markings (not shown) become submerged and are permanently fixed in the coating. The coating takes on a glossy appearance, loses its abrasive quality, and be comes diiiicult to write upon.

The marking qualities of various marking media before and after fixing are tabulated in Table I. Additional marking of an already Iglossed composition is difficult. Erasure of markings after heating is also difeult.

T arble I Ease of Marking and Erasing Mark Erase Additional Material before before marking Erasure of glossing glossing after fixed mark glossing Graphite (pencil) Carbowax (crayon) lnk Silver (coin) Copper (coin) Nickel (coin) Charcoal Wax (paran) i The support for the coating composition may be of any suitable material. Some suitable support materials are metals such as iron, copper, aluminum and silver; cellulosic materials such as paper, cellophane and Wood; and other materials 1as textiles, glass, ceramic or mineral block. The support may be a sheet, web or foil, or may be massive.

Any inorganic pigment used or usable in the paper coating arts may be used herein. he pigment may be colored or colorless. The pigment preferably should have a melting point higher than that of the vehicle land lowrnelting material. Examples of suitable inorganic pigments are titanium dioxide, stannic oxide, zinc sulde, zinc oxide, iron oxide, and cadmium sulfide-zinc sulde fluorescent pigment.

The low-melting material may be a material of any composition which (1) has a low-melting point, preferably a sharp melting point between 75 Vand 200 C., (2) preferably produces low viscosity materials upon melting, and (3) hardens to produce a glossy surface. The melting point of the low-melting material is preferably within C. of the softening point of the vehicle. Further, to simplify fabrication the low-melting material should be substantially insoluble in the solvent for the vehicle. Some suitable low-melting materials are shown in Table II.

Table Il LOW-MELTING MATERIALS Approximate melt- Materral: ing point, C.

Soaps- Calcium stearate Aluminum stearate -8 156 Aluminum stearate -6 112 Magnesium stearate 146l Zinc stearate 119 Napalm (aluminum soaps of naphthalenic acids. Waxes- Castorwax 1 (l2-hydroxy stearin) 86 Carnauba (natural Wax) 82 Ultracera Amber (microcrystalline Wax of Bareco Oil Co., Barnsdall, Oklahoma) 94 Polymekon (chemically modified microcrystalline wax of Warwick Wax Co., New York, N.Y.) 100 Petronauba D (microcrystalline Wax of Bareco Oil Co.) 82

Polymerized petroleum resins--Piccopale.1 Copolymer of modified styrene---Piccotex-1 Acrylic ester resin--Acryloid B-72.1

lChemical tradename-see W, Haynes, Chemical Trade- ItnarkKsI :trintggnnnercial Synonyms, D. Van Nostrand, Princeon, l. o

Table III VEHICLES Material: i Appiriigbndilnt ogen- P1ccopalel00 1 (polyme-rrzed petroleum resin) 100 Piccotex 1 (copolymer of modified styrene) 115 Acryloid B-72 1 (acrylic ester resin).

1Chemical tradename-see W. Haynes, op. cit.

The vehicle may be any vehicle ordinarily usable with the pigment selected` It is preferred that the vehicle has a softening point Within about 100 C. of the melting point of the low-melting material so that, upon heating, the low melting material may pass easily to the surface of the composition. Further, it is preferred that the vehicle be soluble in a solvent in which the low-melting material and the pigment are substantially insoluble. Some suitable solvents for the mix of Example l are toluene, xylene and ethyl alcohol. Some suitable vehicles are shown in Table III. Y

The glossing and fixing operations of the compositions herein may be explained in one or more of the following ways. One explanation is illustrated in FIGURES 1(11) and 1(17). Upon heating, the low-melting material 20 merely melts and oats upon the surface of the balance of the composition submerging the pigment particles 22 of the composition below the surface. Effectively, the low-melting material forms a distinct layer 23a with a gloss surface on top of the balance of the composition 23b. This explanation probably applies to waxes which are not compatible with the vehicle.

A second explanation is illustrated in FIGURES l(a) and 1(0). Upon heating, the low-melting Vmaterial 20 melts and dissolves part or all of the Vehicle of the composition thereby increasing the -uid bulk of the coating Z3. The pigment 2.2 then settles in this solution. Upon cooling, the solution solidies forming a new coating 23C with a gloss finish surface. By the second explanation, one or more of the modifiers may also act as an auxiliary solvent or solute during heating.

By a third explanation, the low-melting material and the pigment may set up as an oriented thixotropc structure. The thixotropic structure is lost upon heating and the pigment particles settle below the surface of the coatgBy any explanation, the low-melting material preferably has a melting point above room temperature but below about 200 C. Further, the low-melting material should be particulate in the single coating composition and should be a phase separate from either the pigment or the vehicle. Thus, three phases are present before heating. The term phase, as employed herein and in the appended claim, is defined to mean a homogeneous, physically distinct portion of matter in a non-homogeneous system. After heating either two or three phases are present. By either explanation, pigment particles extend irregularly from the surface imparting a matte finish and abrasiveness to the surface of the composition before heating. After heating, the pigment particles are completely covered with one or more other ingredients of the composition.

In accordance with the foregoing explanations, the pigment, the low-melting material and the vehicle are selected in such proportions as to provide a matte surface finish before heating and a gloss surface finish after heating. The optimum proportions will vary according to the materials selected and the particle size of the materials. Where zinc oxide is the pigment, the proportions may be between about 50 and 90 by Weight percent zinc oxide, up to 20 weight percent low-melting material and the balance being composed of the vehicle. The larger the particle size of the pigment, the greater the proportion of pigment that may be used.

Various modifiers may be added to the basic mix to modify the properties thereof. Often the modifier will also function as a vehicle or as a low-melting material. Materials such as tricresyl phosphate or various resins may be added to affect the electrical properties, iiexibility, toughness or plasticity of the composition. Dyes may be added to modify the color or electrical properties of the composition.

p By one method of preparation, the vehicle is first dissolved in the solvent. Then the low-melting material and the pigment are suspended in the solvent solution. The solvent is selected such that it will dissolve the vehicle but leave the pigment and the low-melting material substantially unaffected. The suspension is then coated on a support, such as paper, and the solvent removed at temperatures below the glossing temperature of the coatmg.

By another method of preparation and referring to FIGURE 2, a recording element herein may comprise coating 20a of a low-melting material (with or Without a vehicle) on a support 21 and an overcoating 24 upon the low-melting coating of a composition comprising a pigment suspended in the vehicle. This feature is illustrated in the following example.

EXAMPLE 2 Prepare a first suspension of:

Grams Acryloid B-72 1 40 Alcohol 250 Toluene 75 and coat the surface of a paper support with the first and coat the second suspension over the first coating. Dry the secondcoating at temperatures below C. The resultant recording element has the appearance of and functions in a manner similar to the recording element of Example l.

Some of the improved recording elements herein may be used as the photosensitive recording element in an electrostatic printing process such as described by C. I. Young and H. G. Greig in Electrofax--Direct Electrophotographic Printing on Paper, RCA Review, volume l5, No. 4, pages 469 to 484 (December 1954). For this purpose, the foregoing teachings apply. However, it is necessary to select the pigment, the low-melting material and vehicle as follows. The vehicle should be electricallyinsulating and film-forming. The low-melting material is preferably present in proportions up to about 10 weight percent of the composition. And, the pigment should be a particulate photoconductor and should be present in proportions between 50 and 90 weight percent of the composition. Where the pigment is a photoconducting zinc oxide, the Zinc oxide should have a value of surface photoconductivity higher than 10F9 ohms-/ square/ watt/cm?. In this expression for surface photoconductivity the term photoconductivity refers to the difference between the conductivity in the dark and the conductivity of a substance in the light. The adjective surface is used to indicate that substantially all of the light is absorbed within a thin layer at the surface of a measured specimen. The term ohms-1 is the conventional measure of conductivity. The term square takes into account the geometry of a measured specimen. Where the area between measurement electrodes is a square, the results are independent of the size of the square. The term /watt/cm.2 expresses the measurement in per unit brightness of light per unit area illuminated.

In the research work to develop the electrophotographic recording elements described in the Young and Greig publication, op. cit., it was noted that several of the zinc oxides tested produced recording elements which did not print or printed very poorly. Most of these zinc oxides were made by the American process directly from zinc ore. Measurements o f the equivalent voltage of the surface immediately after electrostatic charging in the dark indicated little or no retention of surface electrostatic charge. This is believed to be due to the rapid decay of electrostatic charge of coatings made with the zinc oxides. However, such zinc oxides are nevertheless useful in recording elements herein which are not used as the photosensitive element for electrostatic printing. The remaining zinc oxides produce coatings Vwhich do retain sufcient electrostatic charge, may be prepared as described above, and may be used in electrostatic printing processes.

Several tests have been devised to distinguish the zinc oxides which are useful in electrostatic printing because of their photoconducting properties and those which are not. These tests are described as follows.

Test ].-A mixture was prepared comprising about 10 milligrams of dry zinc oxide powder and a few drops of an 80% solution of silicone resin in xylene (GE-SR 82, marketed by the General Electric Company, Silicone Products Division, Waterford, N.Y.) diluted with toluene in the ratio 60 grams solution to 105 grams toluene. The mixture was coated on filter paper and dried to produce a dry coating over an area about 0.25 inch in diameter. The dry coating was cooled to about -190 C. and examined in light from a mercury vapor lamp having a maximum output at about 3650 A. The zinc oxides which produce printable coatings produce a lavender or orange luminescence by this test. Other zinc oxides exhibit a green Yor yellow luminescence.

Test 2.-About 0.25 gram of dry zinc oxide powder was placed in a silica boat. The boat was inserted into a silica tube and the system ilushed with hydrogen gas. The tube and boat were red for about 5 minutes at about 1000 C. in a stagnant hydrogen atmosphere. The boat was cooled in hydrogen to room temperature. The fired zinc oxide was examined in light from a mercury vapor lamp having a maximum output at about 2,650 A. The zinc oxides which produce printable coatings luminesce brightly. Other Zinc oxides luminesce weakly or not at all.

VTable lV compiles the results of the two tests on typical commercially-available zinc oxides and indicates the correlation between tliese tests and the printability of the zinc oxides used in the coatings of the invention. The zinc oxides marked G in column 3 may be used to prepare recording elements for electrostatic printing or for nonphotoconducting uses. The zinc oxides marked P may be used for non-photoconducting uses.

Table IV Zinc Oxide Test 1 Test 2 Test 3 Mallinckrodt: 1

1. Analytical R e a g e n t. lavender bright green G WXAV-l. 2. Analytical R e a g en t or.laveder. -...do G

WYEB. i 3. Ultrapure Y-1000 orange grey green G 4. Ultrapure S-621. light purple bright green G 5. USP XIV lavender do G 6. Analytical R e a g e nt do G WYBA. Eagle-Picher: 2

7. USP d do G G do G P P grey lavender. G

grey green very dull green.. P

green do P 0-.---.-" nearly dead P .do --..do P do do P lavender bright greenm-- G can Proa).

23. Spec. Pure No. 500

24. Florence Green Seal.--

25. Florence Red Seal 26. Florence White Seal-.- .do G 27. C.E. 8099--3 light green. G 28. C.E. 8099-3 dull brown G green. Fischer: i

29. Cat. No. Z-51 tech. yellow very dull green P dry. proc.

30. Cat. No. Z-49 USP steel gray-- bright green. G

dry proc.

31. Cat. No. Z-53 lavender de G See footnotes at end of table.

G-prints Well.

P-prints poorly.

1 Mallinckrodt Chemical Works, New York, N.Y.

2 Eagle-Fieber Sales Co., Philadelphia, Pa.

3 American Zinc Sales Co., New York, N .Y.

4 New `Tersey Zinc Co., Pah-norton Pa.

U Fischer Scientiiic Co., Eimer and Amend C0. Division of New York Spex Industries, Queens Village 27, N.Y.

7 `Tohnson, Matthey and Co., 73 Hatton Garden, London, England.

E Allied Chemical and Dye Corp., General Chemical Division, New York, N .Y.

i G. Frederick Smith Chemical Co., Columbus, Ohio.

Examples l to 1l, 13, 14, 16 and 17 describe recording elements of the invention which are useful in electrostatic printing, as by the methods described in Youn and Greig, op. cit.

EXAMPLE 3 Grams (l) Zinc oxide (Florence Read Seal-8) 120 (2) Calcium stearato 5 (3) Piccopale-lOO 1 38 (4) Toluene 118 (5) Piccolastic A-5 1 5 (5) Tricresyl phosphate 5 A The Piccopale-IOO, Piccolastic A-S and tricresyl phosphate Vwere dissolved in the toluene. The calcium stearate was then added and the slurry warmed to C.1 The calcium stearate goes into colloidal suspension at about this temperature. The zinc oxide was added (after the suspension had cooled) and was dispersed in a Waring Blendor.

Paper was coated with this mix by conventional paper coating techniques but with drying below the temperature that causes glossing. This matte surface paper glossed in the heat xing step at about C. in a few seconds.

EXAMPLE 4 Grams (l) Zinc oxide (Florence Green Seal-8) 120 (2) Napalm 2 (3) Piccopale-IOO 1 38 (4) Toluene 118 (5) Piccolastic A-S l 5 (5) Tricresyl phosphate 5 The Piccopale-lOO, Piccolastic A-5 and tricresyl phosphate were dissolved in the toluene. The napalm was then added and the slurry warmed to 80 C. The napalm goes into colloidal suspension at about this temperature. The zinc oxide was added after the suspension had cooled and was dispersed, as in a Waring Blendor. Paper was coated with this mix by conventional paper coating techniques but with drying below the temperature that causes glossing. This matte surface glossed in the heat fixing step at about 180 in a few seconds.

EXAMPLE 5 Grams l) Zinc oxide (Florence Green Seal-8) 120 (2) Aluminum stearate 5 (3) Piccopale--lOO1 38 (4) Toluene 118 (5) Piccolastic A-5 1 5 (5) Tricresyl phosphate 5 The Piccopale-l00, Piccolastic A-S and tricresyl phos-` 9 phate were dissolved in the toluene. The aluminum stearate was then added and the slurry warmed to 80 C. The aluminum stearate goes into colloidal suspension at about this temperature. The zinc oxide was added after the suspension had cooled and was dispersed as in a Waring Blendor. Paper was coated with this mix by conventional paper coating techniques but with drying below the temperature that causes glossing. This matte surface electrophotographic paper glossed in the heat fixing step at about 180 C. in a few seconds. 10

` EXAMPLE 6 Grams (l) Zinc oxide (Florence Green Seal-8) 120 1) Titanium dioxide (PC3l2-NJ. Zinc Co.) 20 15 (2) Calcium stearate 5 (3) Piccopale-lOO 1 38 (5) Piccolastic A-5 1 5 (5 Tricresyl phosphate 5 (4) Toluene 118 20 The Piccopale, Piccolastic and tricresyl phosphate were first dissolved in the toluene. The Zinc oxide and titanium dioxide and calcium stearate were then added to this solution and dispersed in a Waring Blendor. The temperature was increased to 53 C. Paper was coated by 25 conventional coating techniques and dried without heat. This paper dried to a good matte nish, printed Well by the printing techniques of the Young et al. publication, op. cit., and glossed on heating to about 180 C. for a few seconds.

EXAMPLE 7 Grams (1) Zinc oxide (Florence Green Seal-8) 120 (2) Carnauba wax (No. 1 yellow) 6 35 (3) Piccopale-100 1 38 (5) Piccolastic A-5 1 5 (5) Tricresyl phosphate 5 (4) Toluene 100 40 The Piccopale, Piccolastic and tricresyl phosphate were dissolved in the toluene. The zinc oxide was added and dispersed in the Waring Blendor. The mix was heated to boiling and the carnauba wax added and dissolved. Paper was coated while the mix was still hot. The Wax apparently crystallizes out of solution in a finely-divided phase before the coating sets. The paper had a matte finish and glossed when heated to 180 C. for a few seconds.

EXAMPLE 8 50 Grams (1) Zinc oxide (Florence Green Seal-8) 120 (2) Ultracera amber wax1 (Bareco) 5 (3) Piccopale-lOO 1 38 (5) Piccolastic A-5 1 5 55 (5) Tricresyl phosphate 5 (4) Toluene 100 The Piccopale, Piccolastic and tricresyl phosphate were dissolved in the toluene. The zinc oxide was added and dispersed, as in the Waring Blendor. The mix was heated to boiling and the Ultracera Amber Wax (Bareco) added and dissolved. Paper was coated while the mix was still hot. The wax apparently crystallizes out of solution in a finely-divided phase before the coating sets. The paper had a matte nish and glossed upon heating to about 180 C. in a few seconds. i

EXAMPLE 9 Grams (1) Zinc oxide (Florence Green Seal-8) 120 70 (2) Petronauba D 1 wax (Bareco) 10 (3) Piccopale-1001 38 (5 Piccolastic A5 1 5 (5) Tricresyl phosphate 5 (4) Toluene 100 75 The Piccopale, Piccolastic and tr-icresyl phosphate were dissolved in the toluene. The zinc oxide was added and dispersed, as in the Waring Blendor. The mix was heated to boiling and the Petronauba D was added and dissolved. Paper was coated while the ymix was still hot. The wax apparently crystallizes out of solution in a iinely-divided phase before the coating sets. The paper had a matte finish and glossed upon heating to about 180 C. in a few seconds.

EXAMPLE 10 Grams (1) Zinc Oxide (Florence Green Seal-8) 120 (2) Petronauba D 1 wax (Bareco) 10 (3) Piccopale-1001 38 (5) Piccolastic A-S 1 5 (5) Tricresyl phosphate 5 (4) Toluene 100 EXAMPLE 11 Grams (2) Silicone resin (GE SR-82 60% solids in xylene) (4) Toluene 106 1) Zinc Oxide (Florence Green Seal-8) 120 (3) PetronaubaD1wax (Bareco) 30 EXAMPLE 12 Follow the procedure of Example 1 except substitute the following coating mix:

Grams (l) Stannic oxide 125 (2) Petronauba D 1 wax 18 (3) Piccopale-1001 resin 38 (4) Toluene 130 (5 Tricresyl phosphate 5 (5) Piccolastic A-5 resin 5 This mix can best be coated at about 50 C. and the s01- vent removed below C.

EXAMPLE 13 Follow the procedure of Example 12 except substitute the following coating mix:

Grams (l) Zinc sulfide (ZS-800 of NJ. Zinc Co., Palmerton, Pa.) (2) Petronauba D 1 wax 23 (2) Magnesium stearate 2.5 (3) Piccopale-1001 resin 38 (4) Toluene 130 (5 Tricresyl phosphate 5 (5) Piccolastic A-S resin 5 EXAMPLE 14 Follow the procedure of Example 12 except substitute the following coating mix:

Grams (l) Cadmium sulfide-zinc sulfide fluorescent pigment 125 (2) Petronauba D 1 wax 18 (3) 'P-iccopale-lOO 1 resin 38 (4) Toluene 130 (5) Tricresyl phosphate 5 (5) Piccolastic A-S resin 5 11 EXAMPLE Follow the procedure of Example 12 except substitute the following coating mix:

Grams (l) Micronized magnetite (iron oxide) 250 (2) Petronauba D 1 wax 18 (3) lf'iccopale-IOO1 resin 38 (4) Toluene 130 (5) Tricresyl phosphate 5 (5) Piccolastic A-5 resin 5 EXAMPLE 16 Follow the procedure of Example 12 except substitute the following coating mix:

. Grams (l) Stannic oxide 125 (2) Petronauba D 1 wax 21 (2) Magnesium stearate 3 (3) Piccotex 1 38 (4) Toluene 130 (5) Tricresyl phosphate 5 (5) Piccolastic A-5 resin 5 EXAMPLE 17 Prepare a coating mix of the following composition:

Grams (i) Zinc oxide (Florence Green Seal-8) 100 (2) Castorwax (IZ-hydroxystearin) 32 (3) Acryloid 12a-721 resin 40 (4) Ethyl alcohol 250 (4) Toluene 75 Dissolve the acryloid resin in the ethyl alcohol and toluene. Disperse the zinc oxide in the resin solution. Then disperse the castorwax in the suspension with warming. The mix is then coated on a metai plate or a paper sheet at about 60 C. and air dried at room temperature.

In the foregoing examples, the superscript (l) indicates a tradenarne more fully identified in W. Haynes, op. cit.

Ey way of example, and referring to FIGURE 3, the recording element of Example 1 may be used in an electrostatic printing process according to the following steps. The recording element of Example 1 is placed with the backing 21 upon a grounded metal plate 25 and in darkness, an electrostatic charging device 51 passed over the photoconducting coating 23 to provide an electrostatic charge thereon. The charging device 51 may comprise an array of line wires 53 mounted near the grounded metal plate 25. A source of D.C. voltage is connected between the wires 53 and the grounded plate 2S to provide a negative charge on the Wires with respect to grounded plate 2S. The voltage should be sufficiently high to cause a corona discharge adjacent the wires. It is preferred to apply about 6000 volts with respect to ground to the wires 53 when charging the surface of the recording element of Example l. The surface of the recording element passing under the charging device 51 becomes charged negatively when the preferred voltage applied. The apparatus and process may produce a blanket positivey charge if the polarity of the wires 53 is positive with respect to the grounded plate 25.

The next step in the process is to discharge selected areas 'of the charged surface of the recording element in order to produce an electrostatic image thereon. Refering to FIGURE 4, this may be accomplished by placing a photographic transparency 61 upon the charged surface of the coating 23 and exposing to light derived, for example, from a lamp 59 in the manner of conventional contact printing. An exposure of about 1 second from a 100 watt tungsten lamp about 24 inches from the recording element for a normal density photographic transparency hasbeen found'to be adequate. The light image may be produced by any of the ordinary photographic processesasUby-projection,contact, or reflux. Any type of electromagnetic radiation may be used provided a portion thereof falls within the spectral sensitivity of the photoconducting coating 23. In the example, visible blue and ultraviolet light may be used. For other photoconducting strata, visible light, infra-red, ultraviolet or X- rays may be used. Wherever the light strikes the surface of the photoconducting coating 23, the electrostatic charge thereon is reduced or removed. This leaves an electrostatic image or pattern of charges corresponding to the non-illuminated areas of the light image.

The electrostatic image may be stored for a time if desired. Ordinarily the next step is to develop the electrostatic image with a finely-divided developer substance such as a finely-divided powder or an ink mist. Referring to FIGURE 5, development of the electrostatic image is preferably accomplished by maintaining the recording element in darkness and passing a developer brush 59 containing a developer powder across the surface of a photoconducting coating 23 bearing the electrostatic image. Areas 27 of developer powder are deposited on those areas of the surface retaining an electrostatic charge. The developer brush comprises a mixture of magnetic carrier particles, for example powdered iron, and the developer powder. The mixture is secured in a magnetic field by a magnet 57 to form a developer brush.

A preferred carrier material for the developer mix consists of alcoholized iron, that is, iron particles free fom grease and other alcohol-soluble impurities. These iron particles are preferably relatively small in size, being in their largest dimension about .002" to .008. Satisfactory results are also obtained using a carrier consisting of iron particles of a somewhat wider range of sizes from about .001 to .020.

A preferred developer powder may be prepared as follows: A mixture comprising 200 grams of 200 mesh Piccolastic resin 4358 (an elastic thermoplastic resin composed of polymers of styrene, substituted styrene andits homologs), marketed by the Pennsylvania Industrial Company, Clairton, Pa., 12 grams of Carbon Black G, marketed by the Eimer and Amend Co., New York, N.Y.,

2 grams of spirit Nigrosine S.S.B., marketed by the Allied Chemical and Dye Co., New York, N.Y., and 8 grams of Iosol Black, marketed by the Allied Chemical and Dye Co., New York, N.Y., are thoroughly mixed in a stainless steel beaker at about 200 C. The mixing and heating should be done in as short a time as possible. The melt is poured into a brass tray and allowed to cool and harden. The hardened mix is then broken up and ball-milled for about 20 hours. The powder is screened through a. 200 mesh screen and is then ready for use as a developer powder. This powder takes on a positive electrostatic charge when mixed with glass beads or iron powder. It therefore develops an electrostatic image composed of negative charges. Two to four grams of the developer powder and grams of the magnetic carrier material are blended together giving the preferred developer mix. Other ratios may be used.

The developer powder may be chosen from a large class of material-ls. The developer powder is preferably electrically-charged to aid 4in the development of the electrostatic latent image. The powder may be electricallycharged because the powder (l) is eleotroscopic, or (2) has interacted with other particles with which it is triboelectrically active or (3) has been charged from an electric source such as a corona discharge. Examples of suitable developer powders are powdered zinc, powdered copper, carbon, sulfur, pigmented natural and synthetic resinsor mixtures thereof.

The developer powder may -be applied tothe electrostatic image in other Ways, for example, it may be dusted on' to -the image, or it may be mixed with `glass beads, magnetite, or other suitable carrier particles, and the mixture then brought i-nto contact with the-surface of the photoconducting stratum. The'beads serve merely as a temporary carrier, releasing the powder particles upon contact with the charged surface.

The type of developer powder described is a positivelycharged powder and will adhere readily to negativelycharged areas of the electrostatic image. -In the developed image described, the developed areas 4of the image correspond to the non-illuminated portions of the light image. I the photoconducting coating 23 is charged positively, and the same steps are carried through as above-described, a reverse image is obtained. If a negatively-charged powder is used in place of -the positivelycharged powder, then a reverse image is obtained in the rst case and a positive image is obtained in the alternative case. y

The developed image is now fixed to the photoconducting coating. This is easily accomplished with the recording element of the invention. One merely places ythe recording element with the powder image thereon in an oven or under an infra red lamp and applies heat above 100 C. to the surface. The recording element is converted yto a glossy appearance and the powder image is fixed to the surface threeof as described above.

The recording elements herein may also be used in an electrostatic printing process as a heat fixing transfer medium. ln U. S. Patent No. 2, 297,691 to C. F. Carlson, there is described electrostatic printing processes where a powder image of a desired configuration is prepared upon a selenium plate, and the powder image then transferred to a suitable medium and tixed thereon. Adhesives or thermoplastic powders are suggested for xing. When the recording elements herein are used as transfer media in the Carlson processes, the powder image need not be of a thermoplastic material. Also, adhesives are unnecessary. Instead, upon transfer of the powder image to a recording element herein, heat is applied glo-ssing the surface and xing the powder image thereon.

There have been described improved compositions for recording elements which are prepared with a matte surface iinish and which may be subsequently converted to a glossy linish by the application of heat. The recording elements herein are adapted to -receive information and upon the application of heat, x the information already recorded and prevent the addition of [further linformation thereto. There have further been described methods for preparing such compositions and methods for preparing the recording elements of the invention.

What is claimed is:

A method of recording on a coated electrophotographic element having a .matte surface, the coating on said element comprising from to 90% by weight of a linelydivided photoconductor suspended in and protruding above the surface of an electrically-insulating, film-forming, thermoplastic vehicle, said coating including 1.2% to 20% by weight of a low-melting material insoluble in said vehicle and having a melting point between about C. and 200 C., said vehicle having a softening point not more than C. above said `melting point, sai-d vehicle, photoconductor, and low-melting material comprising three distinct separate phases; said method comprising the steps of: electrophotographically producing a latent electrostatic image on said coating, producing a visible image on said coating by applying thereto a finelydivided developer substance, and heating said coating to a temperature at least equal to the softening point temperature of said vehicle to fix said developer substance to said coating and to convert said matte surface to a gloss sunface.

References Cited in the le of this patent UNITED STATES PATENTS 2,069,648 Stose Feb. 2, 1937 2,116,986 Denner May 10, 1938 2,275,957 Grol Mar. 10, 1942 2,287,348 Hayden June 23, 1942 2,346,624 Straus Apr. l1, 1944 2,380,126 Sturm July 10, 1945 2,471,870 Gidley May 31, 1949 2,490,550 Sermattei Dec. 6, 1949 2,554,017 Dalton May 22, 1951 2,566,516 Derby Sept. 4, 1951 2,619,440 Lord Nov. 25, 1952 2,663,636 Middleton Dec. 22, 1953 2,705,682 Willie Apr. 5, 1955 2,758,939 Sugarman Aug. 14, 1956 2,776,907 Carlson Jan. 8, 1957 2,855,324 Van Dorn Oct. 7, 1958 2,875,054 Greig et al Feb. 24, 1959 FOREIGN PATENTS 201,301- Australia Mar, 19, 1956 203,907 Australia Nov. 1, 1956 OTHER REFERENCES Young et al.: R. C. A. Review, December 1954, pages 469-484.

Bennett: Commercial Waxes, Chemical Publishing Co. (1956), page 269. 

